1. Technical Field
This disclosure relates generally to a liquid container that stores a liquid such as ink to supply the ink to a recording head and so forth that discharges the ink as droplets from, for example, nozzles of the recording head onto a recording medium to form an image on the recording medium. This disclosure further relates generally to a liquid droplet discharging device including the liquid container, and an image forming apparatus including the liquid droplet discharging device.
2. Description of the Background
Related-art image forming apparatuses such as copiers, printers, facsimile machines, and multifunction devices having two or more of copying, printing, and facsimile functions include inkjet-type image forming apparatuses employing a liquid discharge recording method. Based on image data, such inkjet-type image forming apparatuses discharge ink droplets from nozzles of recording heads onto a recording medium such as a sheet of paper to form an image on the sheet.
Inkjet-type image forming apparatuses generally include a large-capacity main cartridge or main tank in a main body thereof. Ink or other such recording liquid is supplied from the main tank to a small-capacity sub-tank to replenish the small-capacity sub-tank, which serves as a recording liquid container provided on a carriage and supplies ink to the recording heads. Alternatively, inkjet-type image forming apparatuses may include an ink cartridge itself serving as the recording liquid container that can be replaced with a new ink cartridge together with the recording head.
Inkjet-type image forming apparatuses having the sub-tank are further supplied with a supply tube through which the ink is supplied from the main tank to the sub-tank and a flexible film member serving as a damper that prevents pressure fluctuation in the sub-tank. Long-term use of the supply tube and the flexible film member gradually allows penetration of air, and eventually, the air accumulates within the sub-tank. Further, a slight amount of air enters the main tank due to attachment and detachment of the main tank to and from the main body of the inkjet-type image forming apparatuses. Ultimately, the air within the main tank enters the sub-tank as the ink is supplied from the main tank to the sub-tank.
Published Unexamined Japanese Patent Application No. 2005-138472 (hereinafter referred to as JP-2005-138472-A) discloses a pressure release mechanism that releases air from a sub-tank. FIG. 1 is a vertical cross-sectional view illustrating a configuration of a pressure release mechanism 400 disclosed in JP-2005-138472-A. The pressure release mechanism 400 is detachably attached to a container body 501 that stores ink supplied to the sub-tank, and includes a holder 402 having, at a leading edge thereof, a pressure release hole 401 connected to an air flow path 503 within the container body 501. The holder 402 includes a valve seat 423 composed as a cylindrical gasket, a ball 424 serving as a valve movable to contact to and separate from the valve seat 423, a coil spring 425 that biases the ball 424 against the valve seat 423, and a biasing pin 427. One end of the biasing pin 427 protrudes outward from the pressure release hole 401 and the other end of the biasing pin 427 faces the ball 424. The biasing pin 427 is pressed by a pressure release pin 601 driven by an external drive unit so as to contact the ball 424 and move the ball 424 away from the valve seat 423 to release air from the sub-tank.
Although the above-described configuration is generally successful, during mounting within the holder 402 the valve seat 423 is compressed in both radial and surficial directions thereof. Consequently, when the center of the pressure release hole 401 of the holder 402 and the center of the cylindrical valve seat 423 are not perfectly aligned, an inner diameter of the valve seat 423 is deformed, and the valve seat 423 does not completely contact the ball 424, allowing air to leak. As a result, negative pressure is not kept in the sub-tank, resulting in irregular discharge of ink droplets.
Although a contact state or seal between the ball 424 and the valve seat 423 may be tested by a pressure proof test and so forth, even an unstable seal between the ball 424 and the valve seat 423 may pass the pressure proof test because the test is performed only once.
Further, because the holder 402 including the valve seat 423, the ball 424, and the coil spring 425 is rotated to be attached to the container body 501, the valve seat 423 included in the holder 402 may be twisted upon attachment of the holder 402 to the container body 501, degrading the seal between the ball 424 and the valve seat 423.
A pick may be provided to the holder 402 to attach the holder 402 to the container body 501 without rotating the holder 402. However, because pressure applied to the valve seat 423 caused by pressure from the ball 424 pressed by the coil spring 425 is constantly applied to the pick, thermal deformation or deterioration of the pick may occur over time, resulting in insufficient stability of attachment of the holder 402 to the container body 501.